Year	Percent
1971	6.61
1972	6.35
1973	5.11
1974	3.35
1975	4.3
1976	7.78
1977	8.57
1978	6.73
1980	7.48
1981	8.56
1982	8.59
1983	6.73
1984	10.04
1985	8.14
1986	8.86
1987	10.88
1988	9.52
1989	10.29
1990	9.85
1991	12.8294
1992	11.5361
1993	10.7154
1994	10.5656
1995	10.678
1996	9.7495
1997	9.8204
1998	10.9805
1999	9.9985
2000	11.5987
2001	4.0182
2002	12
2003	3.8421
2004	3.8893
2005	4.1998
2006	4.3304
2007	3.7157
2008	4.0061
2009	4.1313
2010	3.7891
2011	3.8279
2012	3.7329
2013	3.823
2014	3.7244
2016	2.8703
2017	2.7027